Bits Manipulation
Bit manipulation is the act of algorithmically manipulating bits or other pieces
of data shorter than a byte. C language is very efficient in manipulating bits.
Here are following operators to perform bits manipulation:
Bitwise Operators:
Bitwise operator works on bits and perform bit by bit operation.
Assume if B = 60; and B = 13; Now in binary format they will be as follows:
A = 0011 1100
B = 0000 1101

A&B = 0000 1000
AB = 0011 1101
A^B = 0011 0001
~A = 1100 0011
Show Examples
There are following Bitwise operators supported by C language
Operator 
Description 
Example 
& 
Binary AND Operator copies a
bit to the result if it exists in both operands. 
(A & B) will give 12 which
is 0000 1100 
 
Binary OR Operator copies a
bit if it exists in either operand. 
(A  B) will give 61 which
is 0011 1101 
^ 
Binary XOR Operator copies
the bit if it is set in one operand but not both. 
(A ^ B) will give 49 which
is 0011 0001 
~ 
Binary Ones Complement
Operator is unary and has the effect of 'flipping' bits. 
(~A ) will give 60 which is
1100 0011 
<< 
Binary Left Shift Operator.
The left operands value is moved left by the number of bits specified by
the right operand. 
A << 2 will give 240 which
is 1111 0000 
>> 
Binary Right Shift Operator.
The left operands value is moved right by the number of bits specified
by the right operand. 
A >> 2 will give 15 which is
0000 1111 
The shift operators perform appropriate shift by operator on
the right to the operator on the left. The right operator must be positive. The
vacated bits are filled with zero.
For example: x << 2 shifts the bits in x by 2 places to the left.
if x = 00000010 (binary) or 2 (decimal)
then:
x >>= 2 => x = 00000000 or just 0 (decimal)
Also: if x = 00000010 (binary) or 2 (decimal)
then
x <<= 2 => x = 00001000 or 8 (decimal) 
Therefore a shift left is equivalent to a multiplication by
2. Similarly a shift right is equal to division by 2. Shifting is much faster
than actual multiplication (*) or division (/) by 2. So if you want fast
multiplications or division by 2 use shifts.
To illustrate many points of bitwise operators let us write a function,
Bitcount, that counts bits set to 1 in an 8 bit number (unsigned char) passed as
an argument to the function.
int bitcount(unsigned char x)
{
int count;
for ( count=0; x != 0; x>>=1);
{
if ( x & 01)
count++;
}
return count;
} 
This function illustrates many C program points:

for loop not used for simple counting operation.

x >>= 1 => x = x>> 1;

for loop will repeatedly shift right x until x becomes 0

use expression evaluation of x & 01 to control if

x & 01 masks of 1st bit of x if this is 1 then count++
Bit
Fields
Bit Fields allow the packing of data in a structure. This is especially useful
when memory or data storage is at a premium. Typical examples:
C allows us do this in a structure definition by putting :bit
length after the variable. For example:
struct packed_struct {
unsigned int f1:1;
unsigned int f2:1;
unsigned int f3:1;
unsigned int f4:1;
unsigned int type:4;
unsigned int my_int:9;
} pack; 
Here the packed_struct contains 6 members: Four 1 bit flags
f1..f3, a 4 bit type and a 9 bit my_int.
C automatically packs the above bit fields as compactly as possible, provided
that the maximum length of the field is less than or equal to the integer word
length of the computer. If this is not the case then some compilers may allow
memory overlap for the fields whilst other would store the next field in the
next word.
NEXT >> PreProcessors
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